Hips hurting and 'locking up'

Has anyone else been experiencing this? I decided to make myself walk around Target for some exercise in hopes I can speed up the process of going into labor. I planned on walking for quite a while but lasted maybe a half hour before my hips started hurting Really bad..Im fine until I lift one of my legs up while walking then that hip will hurt super bad and feel like I can't hardly move it and feels like it's going to lock up. When I lower my leg it doesnt hurt nearly as bad though. I'm sure I looked ridiculous gimping around but it was a little scary! Wondering if anyone knows why this is happening all of a sudden..I'm a couple days away from my 40 week mark